What next after failed sanctions on Iran?

Unfortunately, the new sanctions are unlikely to be any more effective than the first two rounds.

Consider the two earlier Security Council resolutions. The December 2006 resolution curbed international assistance to Iran in mastering the nuclear fuel cycle. The March 2007 resolution called for "vigilance and restraint" in the sale of heavy weapons to Iran and avoidance of new grants, financial assistance, or concessional loans. Neither moved the country's ruling mullahs. Few expect a different outcome from the new sanctions, which authorize international interception of Iranian contraband and tightened monitoring of the regime's financial institutions, along with travel limitations and asset freezes applied to people and companies involved in Iran's nuclear program.